What is DNA?
DNA stands for Deoxyribonucleic Acid, and it is an inherited material found in all living species, from unicellular to multicellular organisms.
DNA is an organic compound having a unique molecular structure. They can be found in both eukaryotic and prokaryotic cells of organisms. It is defined as a group of molecules which carry out the transmission of hereditary materials from parents to their offspring. DNA is also responsible for protein production in living species.
Discovery of DNA
DNA was first identified by Friedrich Meischer in 1869, a Swiss botanist during his examination of a white blood cell. He named it ‘Nuclein’. Following this James Watson and Francis Crick proposed a very simple but famous Double Helix model for the structure of DNA in 1953.
Structure of DNA
DNA is a twisted two-stranded molecule, giving it a unique shape referred to as the double helix. Each strand possesses a backbone. The backbone is made of alternating sugar (deoxyribose) and phosphate groups. Each strand is a long nucleotide sequence. The individual units of DNA are made up of:
- A phosphate molecule
- A sugar molecule called deoxyribose
- A nitrogen-containing region
There are Four types of nitrogen-containing regions called bases includes:
- Adenine(A)
- Cytosine(C)
- Guanine(G)
- Thymine(T)
The order formed by these four bases is the genetic code, which is instructions for life. Two strands of DNA containing bases are joined together to form a ladder-like structure. A stick to T and G sticks to C to create the “Rungs” in the ladder. The length of the ladder is formed by sugar and phosphate groups.
How DNA is Related to Reproduction?
Types of DNA
There are mainly three different types of DNA found:
A-DNA: This is a right-handed double helix structure and is also similar to B-DNA. Dehydrated DNA takes the A form in extreme conditions of desiccation. The protein binding leads to the removal of solvents from the DNA.
B-DNA: This is a right-handed helix structure and is the most common form in DNA. This one exists the most under normal physiological condition.
Z-DNA: This is a left-handed helix structure. It plays some or other roles in the regulation of genes.
The table below shows the differences between B DNA and Z DNA.
| B DNA |
Z DNA |
| What it is | |
| The term B-DNA refers to the canonical right-handed DNA helix, which is the most common type of DNA. | Z-DNA is a left-handed helical form of DNA in which the double helix structure winds to the left in a zigzag pattern. |
| Helical type | |
| Right-handed | Left-handed |
| Occurrence | |
| Common | Less common comparatively |
| Description of major and minor groove | |
| Major groove – wide and deep
Minor groove – narrow and deep |
Major groove – narrow and deep
Minor groove – wide and shallow |
| Condition for formation | |
| Normal physiological condition | High salt concentration |
| Repeating unit | |
| Mononucleotides (1 bp) | Dinucleotides (2 bp) |
| Arrangement of sugar residues | |
| Altering | Not altering |
| Helical diameter | |
| 20 Å | 18 Å |
| Glycosyl angle | |
| anti | C: anti, G: syn |
| Base pairs per turn | |
| 10.5 | 12 |
| Helical pitch | |
| 34 Å | 45 Å |
| The angle of twist per repeating unit | |
| 36° | 60° |
Functions of DNA
Genes are small segments of DNA that typically consist of 250-2 million base pairs. DNA leads to protein formation and transmission of genetic information. Along with this DNA carries out following function:
- Mutation
- Transcription
- Translation
- Replication
- Gene expression
How does DNA work?
Most DNA lives in the nuclei of cells, and some exist in power houses of cells known as mitochondria. DNA needs to be packaged neatly because humans have a lot of DNA and the nuclei are comparatively small. DNA is nearly 3 billion bases long, and 99 percent of those bases are the same in all people. Strands of DNA loop, coil, and wrap around proteins are known as histones. They bind to DNA and help to give chromosomes the desired shape and control the activity of genes.
Chromatin is further condensed through a supercoiling process and then packed into structures called chromosomes. “X”shape is formed by these chromosomes. Each chromosome contains one DNA molecule. Humans have 23pairs of chromosomes or in total 46 chromosomes.
What is gene?
Gene is a hereditary unit passed on from parents to offspring. Each gene contains a specific protein that codes for length of DNA. Humans have around 30,000 genes, estimation vary. For example, one gene code for protein insulin, the hormone that helps in controlling levels of sugar in blood.
Chromosome 1 is the largest, with approximately 2,800 genes. Chromosome 22 is the smallest and contains 750 genes.
Why is DNA Negatively Charged?
The phosphate groups that comprise each nucleotide (pentose + nitrogenous base + phosphate) are the primary cause of DNA’s negative charge. DNA is a nucleotide polymer. They are joined together by a type of covalent bond known as phosphodiester bonds, which can span millions of nucleotides. The phosphate backbone is charged negatively, due to the presence of bonds created by oxygen and phosphorous atoms. Referring to the DNA structure, only one oxygen atom is present in phosphate groups which are negative. However, this one atom makes the complete structure negative.
FAQ’s
Here are some questions about DNA
Who discovered DNA?
The DNA is discovered by a Swiss scientist Friedrich Miescher in 1869, while examining white blood cells.
What are the different types of DNA?
There are many types of DNA each with a specific structure. Most common DNA found is B-DNA. Other types of DNA that are found in the genome includes A-DNA, Z-DNA, H-DNA and many more.
How does DNA affect health?
When a person’s DNA sequence changes randomly it is called mutation. Some changes in a person’s genetic code can result in the development of diseases or conditions. Diseases that result from damage in only one gene are Cystic Fibrosis and Huntington’s Disease. Diseases such as cancer are due to damage in several parts of a person’s DNA.
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